jgit/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/pack/BinaryDelta.java

/*
 * Copyright (C) 2007, Robin Rosenberg <robin.rosenberg@dewire.com>
 * Copyright (C) 2006-2007, Shawn O. Pearce <spearce@spearce.org> and others
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Distribution License v. 1.0 which is available at
 * https://www.eclipse.org/org/documents/edl-v10.php.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */

package org.eclipse.jgit.internal.storage.pack;

import org.eclipse.jgit.internal.JGitText;
import org.eclipse.jgit.util.QuotedString;
import org.eclipse.jgit.util.RawParseUtils;

/**
 * Recreate a stream from a base stream and a GIT pack delta.
 * <p>
 * This entire class is heavily cribbed from <code>patch-delta.c</code> in the
 * GIT project. The original delta patching code was written by Nicolas Pitre
 * (&lt;nico@cam.org&gt;).
 * </p>
 */
public class BinaryDelta {
	/**
	 * Length of the base object in the delta stream.
	 *
	 * @param delta
	 *            the delta stream, or at least the header of it.
	 * @return the base object's size.
	 */
	public static long getBaseSize(byte[] delta) {
		int p = 0;
		long baseLen = 0;
		int c, shift = 0;
		do {
			c = delta[p++] & 0xff;
			baseLen |= ((long) (c & 0x7f)) << shift;
			shift += 7;
		} while ((c & 0x80) != 0);
		return baseLen;
	}

	/**
	 * Length of the resulting object in the delta stream.
	 *
	 * @param delta
	 *            the delta stream, or at least the header of it.
	 * @return the resulting object's size.
	 */
	public static long getResultSize(byte[] delta) {
		int p = 0;

		// Skip length of the base object.
		//
		int c;
		do {
			c = delta[p++] & 0xff;
		} while ((c & 0x80) != 0);

		long resLen = 0;
		int shift = 0;
		do {
			c = delta[p++] & 0xff;
			resLen |= ((long) (c & 0x7f)) << shift;
			shift += 7;
		} while ((c & 0x80) != 0);
		return resLen;
	}

	/**
	 * Apply the changes defined by delta to the data in base, yielding a new
	 * array of bytes.
	 *
	 * @param base
	 *            some byte representing an object of some kind.
	 * @param delta
	 *            a git pack delta defining the transform from one version to
	 *            another.
	 * @return patched base
	 */
	public static final byte[] apply(byte[] base, byte[] delta) {
		return apply(base, delta, null);
	}

	/**
	 * Apply the changes defined by delta to the data in base, yielding a new
	 * array of bytes.
	 *
	 * @param base
	 *            some byte representing an object of some kind.
	 * @param delta
	 *            a git pack delta defining the transform from one version to
	 *            another.
	 * @param result
	 *            array to store the result into. If null the result will be
	 *            allocated and returned.
	 * @return either {@code result}, or the result array allocated.
	 */
	public static final byte[] apply(final byte[] base, final byte[] delta,
			byte[] result) {
		int deltaPtr = 0;

		// Length of the base object (a variable length int).
		//
		int baseLen = 0;
		int c, shift = 0;
		do {
			c = delta[deltaPtr++] & 0xff;
			baseLen |= (c & 0x7f) << shift;
			shift += 7;
		} while ((c & 0x80) != 0);
		if (base.length != baseLen)
			throw new IllegalArgumentException(
					JGitText.get().baseLengthIncorrect);

		// Length of the resulting object (a variable length int).
		//
		int resLen = 0;
		shift = 0;
		do {
			c = delta[deltaPtr++] & 0xff;
			resLen |= (c & 0x7f) << shift;
			shift += 7;
		} while ((c & 0x80) != 0);

		if (result == null)
			result = new byte[resLen];
		else if (result.length != resLen)
			throw new IllegalArgumentException(
					JGitText.get().resultLengthIncorrect);

		int resultPtr = 0;
		while (deltaPtr < delta.length) {
			final int cmd = delta[deltaPtr++] & 0xff;
			if ((cmd & 0x80) != 0) {
				// Determine the segment of the base which should
				// be copied into the output. The segment is given
				// as an offset and a length.
				//
				int copyOffset = 0;
				if ((cmd & 0x01) != 0)
					copyOffset = delta[deltaPtr++] & 0xff;
				if ((cmd & 0x02) != 0)
					copyOffset |= (delta[deltaPtr++] & 0xff) << 8;
				if ((cmd & 0x04) != 0)
					copyOffset |= (delta[deltaPtr++] & 0xff) << 16;
				if ((cmd & 0x08) != 0)
					copyOffset |= (delta[deltaPtr++] & 0xff) << 24;

				int copySize = 0;
				if ((cmd & 0x10) != 0)
					copySize = delta[deltaPtr++] & 0xff;
				if ((cmd & 0x20) != 0)
					copySize |= (delta[deltaPtr++] & 0xff) << 8;
				if ((cmd & 0x40) != 0)
					copySize |= (delta[deltaPtr++] & 0xff) << 16;
				if (copySize == 0)
					copySize = 0x10000;

				System.arraycopy(base, copyOffset, result, resultPtr, copySize);
				resultPtr += copySize;
			} else if (cmd != 0) {
				// Anything else the data is literal within the delta
				// itself.
				//
				System.arraycopy(delta, deltaPtr, result, resultPtr, cmd);
				deltaPtr += cmd;
				resultPtr += cmd;
			} else {
				// cmd == 0 has been reserved for future encoding but
				// for now its not acceptable.
				//
				throw new IllegalArgumentException(
						JGitText.get().unsupportedCommand0);
			}
		}

		return result;
	}

	/**
	 * Format this delta as a human readable string.
	 *
	 * @param delta
	 *            the delta instruction sequence to format.
	 * @return the formatted delta.
	 */
	public static String format(byte[] delta) {
		return format(delta, true);
	}

	/**
	 * Format this delta as a human readable string.
	 *
	 * @param delta
	 *            the delta instruction sequence to format.
	 * @param includeHeader
	 *            true if the header (base size and result size) should be
	 *            included in the formatting.
	 * @return the formatted delta.
	 */
	public static String format(byte[] delta, boolean includeHeader) {
		StringBuilder r = new StringBuilder();
		int deltaPtr = 0;

		long baseLen = 0;
		int c, shift = 0;
		do {
			c = delta[deltaPtr++] & 0xff;
			baseLen |= ((long) (c & 0x7f)) << shift;
			shift += 7;
		} while ((c & 0x80) != 0);

		long resLen = 0;
		shift = 0;
		do {
			c = delta[deltaPtr++] & 0xff;
			resLen |= ((long) (c & 0x7f)) << shift;
			shift += 7;
		} while ((c & 0x80) != 0);

		if (includeHeader) {
			r.append("DELTA( BASE="); //$NON-NLS-1$
			r.append(baseLen);
			r.append(" RESULT="); //$NON-NLS-1$
			r.append(resLen);
			r.append(" )\n"); //$NON-NLS-1$
		}

		while (deltaPtr < delta.length) {
			final int cmd = delta[deltaPtr++] & 0xff;
			if ((cmd & 0x80) != 0) {
				// Determine the segment of the base which should
				// be copied into the output. The segment is given
				// as an offset and a length.
				//
				int copyOffset = 0;
				if ((cmd & 0x01) != 0)
					copyOffset = delta[deltaPtr++] & 0xff;
				if ((cmd & 0x02) != 0)
					copyOffset |= (delta[deltaPtr++] & 0xff) << 8;
				if ((cmd & 0x04) != 0)
					copyOffset |= (delta[deltaPtr++] & 0xff) << 16;
				if ((cmd & 0x08) != 0)
					copyOffset |= (delta[deltaPtr++] & 0xff) << 24;

				int copySize = 0;
				if ((cmd & 0x10) != 0)
					copySize = delta[deltaPtr++] & 0xff;
				if ((cmd & 0x20) != 0)
					copySize |= (delta[deltaPtr++] & 0xff) << 8;
				if ((cmd & 0x40) != 0)
					copySize |= (delta[deltaPtr++] & 0xff) << 16;
				if (copySize == 0)
					copySize = 0x10000;

				r.append("  COPY  ("); //$NON-NLS-1$
				r.append(copyOffset);
				r.append(", "); //$NON-NLS-1$
				r.append(copySize);
				r.append(")\n"); //$NON-NLS-1$
			} else if (cmd != 0) {
				// Anything else the data is literal within the delta
				// itself.
				//
				r.append("  INSERT("); //$NON-NLS-1$
				r.append(QuotedString.GIT_PATH.quote(RawParseUtils.decode(
						delta, deltaPtr, deltaPtr + cmd)));
				r.append(")\n"); //$NON-NLS-1$
				deltaPtr += cmd;
			} else {
				// cmd == 0 has been reserved for future encoding but
				// for now its not acceptable.
				//
				throw new IllegalArgumentException(
						JGitText.get().unsupportedCommand0);
			}
		}

		return r.toString();
	}
}